Dry etching gas and method for dry etching

ABSTRACT

A dry etching gas that comprises a compound having a CF 3 CF fragment directly bonded to a double bond (provided that the compound is exclusive of CF 3 CF═CFCF═CF 2 ). Said dry etching gas permits the formation of a pattern such as a contact hole with a high aspect ratio.

TECHNICAL FIELD

The present invention relates to a dry etching gas and a dry etching method.

BACKGROUND OF THE INVENTION

With the miniaturization of semiconductor devices, the formation of fine patterns such as contact holes with small hole diameter and high aspect ratio and the like becomes a necessity. Conventionally, contact holes and other patterns have been frequently formed by a gas plasma of c-C₄F₈/Ar(/O₂) containing a large amount of Ar. However, cyclic c-C₄F₈ contributes significantly to global warming, and thus its use is likely to be limited in the future. Further, when not combined with Ar, cyclic c-C₄F₈ is insufficient in the resist selectivity and the silicon selectivity. The etching rate of cyclic c-C₄F₈ varies depending on the pattern size without the addition of a small amount of oxygen, and etching stops under fine pattern conditions. On the other hand, the addition of oxygen lowers the selectivity with regard to the resist and the silicon. It has also been reported that when an excess amount of Ar is blended, the number of high-energy electrons increases, thereby damaging devices.

An object of the present invention is to provide a dry etching gas and a dry etching method, which achieves no reduction in etching rate even when etching small-sized holes, lines or the like; little pattern-size dependency, and the formation of a fine, high-aspect-ratio pattern with no etch stopping through the use of the etching gas that has a substantially small effect on global warming.

DISCLOSURE OF THE INVENTION

The present invention provides the following dry etching gases and dry etching methods.

Item 1. A dry etching gas comprising a compound having a CF₃CF fragment directly bonded to a double bond, with the proviso that CF₃CF═CFCF═CF₂ is excluded.

Item 2. A dry etching gas according to Item 1 comprising a compound represented by the general formula (1): CF₃CF═CXY  (1) wherein X and Y are the same or different, and independently represent F, Cl, Br, I, H or C_(a)F_(b)H_(c) (a=1 to 3, b+c=2a+1). Item 3. A dry etching gas according to Item 1 comprising a compound represented by the general formula (2): CF₃CF═CZ_(2−m)(C_(n)F_(2n+1))_(m)  (2) wherein Z is F, Cl, Br, I, H, CH₃, C₂H₅, C₃H₇, CF₃, C₂F₅ or C₃F₇; m is 0, 1 or 2; and n is 1, 2 or 3. Item 4. A dry etching gas according to Item 3 comprising CF₃CF═CFCF₃. Item 5. A dry etching gas according to Item 1 further comprising at least one member selected from the group consisting of noble gases, inert gases, NH₃, H₂, hydrocarbons, O₂, oxygen-containing compounds, iodine-containing compounds, HFC (hydrofluorocarbons), and PFC (perfluorocarbon) gases having at least one single bond or double bond, with the proviso that the compounds disclosed in Item 1 are excluded. Item 6. A dry etching gas according to Item 1 comprising at least one member of gas selected from the group consisting of noble gases such as He, Ne, Ar, Xe and Kr; inert gases such as N₂ and the like; NH₃; H₂; hydrocarbons such as, CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆ and the like; O₂; oxygen-containing compounds such as CO, CO₂, (CH₃)₂C═O, (CF₃)₂C═O, CF₃CFOCF₂, CF₃OCF₃ and the like; iodine-containing compounds such as CF₃I, CF₃CF₂I, (CF₃)CFI, CF₂═CFI and the like; HFC (hydrofluorocarbons) such as CH₂F₂, CHF₃, CF₃CHF₂, CHF₂CHF₂, CF₃CH₂F, CHF₂CH₂F, CF₃CH₃, CH₂FCH₂F, CF₂═CHF, CHF═CHF, CH₂═CF₂, CH₂═CHF, CF₃CH═CF₂, CF₃CH═CH₂, CH₃CF═CH₂, CH₃CHF₂, CH₃CH₂F, CF₃CF₂CF₂H, CF₃CHFCF₃, CHF₂CF₂CHF₂, CF₃CF₂CH₂F, CF₂CHFCHF₂, CF₃CH₂CF₃, CHF₂CF₂CH₂F, CF₃CF₂CH₃, CF₃CH₂CHF₂, CH₃CF₂CHF₂, CH₃CHFCH₃ and the like; and PFC (perfluorocarbon) gases having at least one single bond or double bond such as CF₂═CF₂, CF₂═CFCF═CF₂, CF₃CF═CFCF═CF₂, c-C₅F₈, CF₄, C₂F₆, C₃F₈, C₄F₁₀, c-C₄F₈ and the like, with the proviso that the compounds disclosed in Item 1 are excluded. Item 7. A dry etching method comprising etching a silicon material such as a silicon oxide film and/or a silicon containing, low-dielectric constant film by means of a gas plasma of a dry etching gas comprising a compound having a CF₃CF fragment directly bonded to a double bond, with the proviso that CF₃CF═CFCF═CF₂ is excluded. Item 8. A dry etching method according to Item 7 wherein the dry etching gas contains a compound represented by the general formula (1): CF₃CF═CXY  (1) wherein X and Y are the same or different, and independently represent F, Cl, Br, I, H or C_(a)F_(b)H_(c) (a=1 to 3, b+c=2a+1). Item 9. A dry etching method according to Item 7 wherein the dry etching gas contains a compound represented by the general formula (2): CF₃CF═CZ_(2−m)(C_(n)F_(2n+1))_(m)  (2) wherein Z is F, Cl, Br, I, H, CH₃, C₂H₅, C₃H₇, CF₃, C₂F₅ or C₃F₇; m is 0, 1 or 2; and n is 1, 2 or 3. Item 10. A dry etching method according to Item 7 wherein the dry etching gas contains CF₃CF═CFCF₃. Item 11. A dry etching method comprising etching a silicon material such as a silicon oxide film and/or a silicon containing, low-dielectric constant film by means of a gas plasma of a dry etching gas comprising: (i) a compound having a CF₃CF fragment directly bonded to a double bond, with the proviso that CF₃CF═CFCF═CF₂ is excluded; and (ii) at least one member selected from the group consisting of noble gases, inert gases, NH₃, H₂, hydrocarbons, O₂, oxygen-containing compounds, iodine-containing compounds, HFC (hydrofluorocarbons), and PFC (perfluorocarbon) gases having at least one single bond or double bond, with the proviso that the compounds disclosed in (i) are excluded. Item 12. A dry etching method according to Item 11 wherein the dry etching gas contains: (i) a compound having a CF₃CF fragment directly bonded to a double bond, with the proviso that CF₃CF═CFCF═CF₂ is excluded; and (ii) at least one member of the gases selected from the group consisting of noble gases such as He, Ne, Ar, Xe and Kr; inert gases such as N₂ and the like; NH₃; H₂; hydrocarbons such as CH₄, C₂H₆, C₃H₈, C₂H₄ and C₃H₆; O₂; oxygen-containing compounds such as CO, CO₂, (CH₃)₂C═O, (CF₃)₂C═O, CF₃CFOCF₂, CF₃OCF₃ and the like; iodine-containing compounds such as CF₃I, CF₃CF₂I, (CF₃)CFI, CF₂═CFI and the like; HFC (hydrofluorocarbons) such as CH₂F₂, CHF₃, CF₃CHF₂, CHF₂CHF₂, CF₃CH₂F, CHF₂CH₂F, CF₃CH₃, CH₂FCH₂F, CF₂═CHF, CHF═CHF, CH₂═CF₂, CH₂═CHF, CF₃CH═CF₂, CF₃CH═CH₂, CH₃CF═CH₂, CH₃CHF₂, CH₃CH₂F, CF₃CF₂CF₂H, CF₃CHFCF₃, CHF₂CF₂CHF₂, CF₃CF₂CH₂F, CF₂CHFCHF₂, CF₃CH₂CF₃, CHF₂CF₂CH₂F, CF₃CF₂CH₃, CF₃CH₂CHF₂, CH₃CF₂CHF₂, CH₃CHFCH₃ and the like; and PFC (perfluorocarbon) gases having at least one single bond or double bond such as CF₂═CF₂, CF₂═CFCF═CF₂, CF₃CF═CFCF═CF₂, c-C₅F₈, CF₄, C₂F₆, C₃F₈, C₄F₁₀, c-C₄F₈ and the like, with the proviso that the compounds disclosed in Item 1 are excluded.

The phrase “a CF₃CF fragment directly bonded to a double bond within its molecule” herein refers to a CF₃CF═C structure.

Dry etching gases usable in the present invention include at least one compound having a double bond within its molecule and having a CF₃CF fragment with the proviso that CF₃CF═CFCF═CF₂ is excluded (hereinafter sometimes referred to as “etching gas components”), preferably include at least one compound represented by the General Formula (1): CF₃CF═CXY  (1) wherein X and Y are as defined above; and preferably at least one compound represented by the General Formula (2): CF₃CF═CZ_(2−m)(C_(n)F_(2n+1))_(m)  (2) wherein Z, m and n are as defined above, more preferably include CF₃CF═CFCF₃. These dry etching gases selectively generate CF₃ ⁺; an etching reaction layer and a protective layer derived from a high-density, even fluorocarbon polymer film are formed by the radicals generated from CF₃CF fragments; and silicon materials such as a silicon oxide film and/or a silicon containing, low-dielectric constant film are etched.

The etching gas components of the invention include those compounds having a CF₃CF fragment directly bonded to a double bond, preferably include at least one compound represented by the general formula (1): CF₃CF═CXY  (1) wherein X and Y are as defined above. Specific examples are CF₃CF═CFCF₃, CF₃CF═CF₂, CF₃CF═C(CF₃)₂, CF₃CF═C(C₂F₅)₂, CF₃CF═C(C₃F₇)₂, CF₃CF═C(CF₃)(C₃F₇), CF₃CF═C(C₂F₅)(C₃F₇), CF₃CF═C(CF₃)(C₂F₅), CF₃CF═CFC₂F₅, CF₃CF═CFC₃F₇, CF₃CF═CFCl, CF₃CF═CClCF₃, CF₃CF═CBrCF₃, CF₃CF═CFBr, CF₃CF═CFI, CF₃CF═CICF₃, CF₃CF═CH₂, CF₃CF═CHF, CF₃CF═CHCF₃, CF₃CF═CHC₂F₅, CF₃CF═CHC₃F₇, CF₃CF═CCHF₂CF₃, CF₃CF═CCHF₂C₂F₅, CF₃CF═CCHF₂C₃F₇, CF₃CF═CCH₂FCF₃, CF₃CF═CCH₂FC₂F₅, CF₃CF═CCH₂FC₃F₇, CF₃CF═CCH₃F, CF₃CF═CCH₃CF₃, CF₃CF═CCH₃C₂F₅, CF₃CF═CCH₃C₃F₇, CF₃CF═CCHFCF₃F, CF₃CF═CCHFCF₃CF₃, CF₃CF═CCHFCF₃C₂F₅, CF₃CF═CCHFCF₃C₃F₇, CF₃CF═CCF₂CHF₂F, CF₃CF═CCF₂CHF₂CF₃, CF₃CF═CCF₂CHF₂C₂F₅, CF₃CF═CCF₂CHF₂C₃F₇, CF₃CF═CCH₂CF₃F, CF₃CF═CCH₂CF₃CF₃, CF₃CF═CCH₂CF₃C₂F₅, CF₃CF═CCH₂CF₃C₃F₇, CF₃CF═CCHFCHF₂F, CF₃CF═CCHFCHF₂CF₃, CF₃CF═CCHFCHF₂C₂F₅, CF₃CF═CCHFCHF₂C₃F₇CF₃CF═CCH₃F, CF₃CF═CCH₃CF₃, CF₃CF═CCH₃C₂F₅ and CF₃CF═CCH₃C₃F₇.

In the compounds represented by the General Formula (1),

a represents an integer of 1 to 3, preferably 1 or 2;

b represents an integer of 0 to 7, preferably 3 to 7; and

c represents an integer of 0 to 7, preferably 0 to 3.

More preferable etching gas components of the invention include at least one compound represented by the general formula (2): CF₃CF═CZ_(2−m)(C_(n)F_(2n+1))_(m)  (2) wherein Z is F, Cl, Br, I, H, CH₃, C₂H₅, C₃H₇, CF₃, C₂F₅ or C₃F₇; m is 0, 1 or 2; and n is 1, 2 or 3.

In the compounds represented by the general formula (2), Z is F, Cl, Br, I, H, CH₃, C₂H₅, C₃H₇, CF₃, C₂F₅ or C₃F₇, preferably, F, I, H, CH₃ or CF₃, more preferably F or CF₃.

In the compounds represented by the general formula (2), m is an integer of 0 to 2, preferably 0 or 1, more preferably 1.

In the compounds represented by the general formula (2), n represents an integer of 1 to 3, preferably 1 or 2, and more preferably 1.

Specific examples of the compounds represented by the General Formula (2) are CF₃CF═CFCF₃, CF₃CF═CF₂, CF₃CF═CFC₂F₅, CF₃CF═CFC₃F₇, CF₃CF═C(CF₃)₂, CF₃CF═C(CF₃)(C₂F₅), CF₃CF═C(CF₃)(C₃F₇), CF₃CF═C(C₂F₅)₂, CF₃CF═C(C₂F₅)(C₃F₇), CF₃CF═C(C₃F₇)₂, CF₃CF═CH₂, CF₃CF═CHF, CF₃CF═CHCF₃, CF₃CF═CHC₂F₅, CF₃CF═CHC₃F₇, CF₃CF═CCH₃F, CF₃CF═CCH₃CF₃, CF₃CF═CCH₃C₂F₅, CF₃CF═CCH₃C₃F₇, CF₃CF═CC₂H₅F, CF₃CF═CC₂H₅CF₃, CF₃CF═CC₂H₅C₂F₅, CF₃CF═CC₂H₅C₃F₇, CF₃CF═CC₃H₇F, CF₃CF═CC₃H₇CF₃, CF₃CF═CC₃H₇C₂F₅, CF₃CF═CC₃H₇C₃F₇, CF₃CF═CFCl, CF₃CF═CCICF₃, CF₃CF═CBrCF₃, CF₃CF═CFBr, CF₃CF═CFI and CF₃CF═CICF₃.

Preferred examples of the dry etching gases of the invention are CF₃CF═CFCF₃, CF₃CF═CF₂, CF₃CF═CFC₂F₅, CF₃CF═C(CF₃)₂, CF₃CF═C(CF₃)(C₂F₅), CF₃CF═C(C₂F₅)₂, CF₃CF═CH₂, CF₃CF═CHF, CF₃CF═CHCF₃, CF₃CF═CHC₂F₅, CF₃CF═CCH₃F, CF₃CF═CCH₃CF₃, CF₃CF═CCH₃C₂F₅, CF₃CF═CFI and CF₃CF═CICF₃.

As the dry etching gas of the invention, the etching gas component may be used in combination with at least one member (hereinafter sometimes referred to as a “combined gas component”) selected from the group consisting of noble gases such as He, Ne, Ar, Xe and Kr; inert gases such as N₂ and the like; NH₃; H₂; hydrocarbons such as CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆ and the like; O₂; oxygen-containing compounds such as CO, CO₂, (CF₃)₂C═O, CF₃CFOCF₂ and the like; iodine-containing compounds such as CF₃I, CF₃CF₂I, (CF₃)CFI, CF₂═CFI and the like; HFC (hydrofluorocarbons) such as CH₂F₂, CHF₃, CF₃CHF₂, CHF₂CHF₂, CF₃CH₂F, CHF₂CH₂F, CF₃CH₃, CH₂FCH₂F, CH₃CHF₂, CH₃CH₂F, CF₃CF₂CF₂H, CF₃CHFCF₃, CHF₂CF₂CHF₂, CF₃CF₂CH₂F, CF₂CHFCHF₂, CF₃CH₂CF₃, CHF₂CF₂CH₂F, CF₃CF₂CH₃, CF₃CH₂CHF₂, CH₃CF₂CHF₂, CH₃CHFCH₃, CF₂═CHF, CHF═CHF, CH₂═CF₂, CH₂═CHF, CF₃CH═CF₂, CF₃CH═CH₂, CH₃CF═CH₂ and the like; and PFC (perfluorocarbon) gases having at least one single bond or double bond between carbon and carbon such as CF₂═CF₂, CF₂═CFCF═CF₂, CF₃CF═CFCF═CF₂, c-C₅F₈, CF₄, C₂F₆, C₃F₈, C₄F₁₀, c-C₄F₈ and the like, with the proviso that the compounds disclosed in Item I above are excluded).

A noble gas such as He, Ne, Ar, Xe, Kr or the like can change the electron temperature and the electron density of the plasma and also has a diluting effect. Through the simultaneous use of such a noble gas, a suitable etching condition can be selected by controlling the balance among fluorocarbon radicals and fluorocarbon ions.

With N₂, H₂ or NH₃ in the combination, excellent etching shape is obtained in the etching of low-dielectric constant films.

Hydrocarbons and HFC improve the etching selectivity by depositing, within the plasma, a carbon-rich polymer film onto the etching-mask, i.e., resist and other underlying layers. Further, HFC itself has an effect of generating ions that are used as etching species.

The term “oxygen-containing compounds” refers to those compounds containing oxygen, for example, CO; CO₂; ketones such as acetone, (CF₃)₂C═O and the like; epoxides such as CF₃CFOCF₂ and the like; and ethers such as CF₃OCF₃ and the like. When these oxygen-containing compounds or O₂ is used in combination, etch-stop is prevented by suppressing the decrease of the etching rate in the etching of fine patterns (microloading effect).

Japanese Unexamined Patent Application No. 340211/1999, Jpn. J. Appl. Rhys. Vol. 39 (2000) pp 1,583-1,596, etc., disclose iodine-containing compounds such as CF₃I, CF₃CF₂I, (CF₃)₂CFI, CF₂CFI and the like. These iodine-containing compounds are preferably used in combination because they are useful for increasing the electron density, and some of them selectively produce CF₃ ⁺.

HFC and PFC that have a double bond within their molecules have little effect on global warming, and such a double bond is likely to dissociate in the plasma, and therefore it is easy to control the generation of radicals and ions necessary in etching.

When, as the dry etching gas of the invention, a mixed gas containing an etching gas component and a combined gas component is used, usually, at least one etching gas component is used in a flow rate of about 10% or more, and at least one combined gas component is used in a flow rate of about 90% or less. Preferably, at least one etching gas component is used in a flow rate of about 20 to about 95%, and at least one combined gas component is used in a flow rate of about 5 to about 80%. Preferable examples of combined gas components include at least one species selected from the group consisting of Ar, N₂, O₂, CO, CF₃I and CH₂F₂.

Table 1 shows a comparison of positive ions and fluorocarbon films formed in the plasma of the preferable dry etching gas of the present invention, i.e., CF₃CF═CFCF₃ and in the plasma of a conventional etching gas, i.e., c-C₄F₈, generated under the discharge incident power of 600 W and pressure of 3 mTorr (0.399 Pa).

TABLE 1 CF_(x) (x = 1 to 3) CF₃ ³⁰ Fluorocarbon radical density content Ra*¹ film (10¹²/cm³) (%) (nm) density *² CF CF₂ CF₃ CF₃CF═CFCF₃ 35 0.8 2.5 × 10⁻⁴ 0.45 0.6 4.0 c—C₄F₈ 19 1.8 2.3 × 10⁻⁴ 0.55 1.2 5.0 *¹Ra: Fluorocarbon film surface roughness (deviation from mean surface roughness, in nanometers). *²Fluorocarbon film density: FT-IR absorbance normalized based on film thickness (maximum peak intensity/film thickness in nanometers).

In plasmas having high dissociation, such as an inductively-coupled plasma and the like used to evaluate the positive ion content and the fluorocarbon films formed in the gas plasmas of CF₃CF═CFCF₃ and c-C₄F₈, most of the positive ions are CF⁺, which have a low etching efficiency, and there are few CF₃ ⁺, which have a high etching efficiency. Conventional gases using c-C₄F₈ generate a relatively large amount of CF₃ ⁺. More CF₃ ⁺ is generated by using CF₃CF═CFCF₃ than by using c-C₄F₈, with the result that CF₃ ⁺ account for 30% or more of the positive ions when CF₃CF═CFCF₃ is used. Although CF₃CF═CFCF₃ generates fewer low-molecular-weight CF_(x) (x=1-3) radicals (among which CF₂ has the highest depositing effect), which serve as primary precursors for fluorocarbon film deposition, than c-C₄F₈ does, the use of CF₃CF═CFCF₃ results in levels of fluorocarbon film evenness that are improved at least twice as much, and film density that is 1.1 times higher per 1 nanometer. These results mean that CF₃ ⁺, which has a high etching efficiency, is generated in the plasma from a CF₃CF fragment and molecules with a structure having a double bond with a weak bond strength, and that fewer polymer radicals are generated and radicals derived from the CF₃CF form high-density, even fluorocarbon films.

Silicon materials such as silicon oxide films and/or silicon containing, low-dielectric constant films may be those films that contain F in a silicon oxide film such as SiOF and the like, silicon nitride films, etc. Silicon materials are not limited to those having a film or layer structure, and include those in which the whole having a silicon-containing chemical formula is composed of the material. A solid material such as glass, quartz plate or the like, can be cited as an example.

Through the use of the dry etching gas of the present invention, silicon materials such as silicon oxide films and/or silicon containing, low-dielectric constant films can be selectively etched in the presence of masks such as resist, polysilicon and the like; underlying layers such as silicon, silicon nitride film, silicide, metal nitride and the like; stopper films such as silicon nitride film, silicon carbide film and the like.

The preferred etching conditions are as follows.

Discharge power: 200 to 3,000 W, and preferably 400 to 2,000 W.

Bias power: 25 to 2,000 W, and preferably 100 to 1,000 W.

Pressure: 30 mTorr (3.99 Pa) or less, and preferably 2 to 10 mTorr (0.266 to 1.33 Pa).

Electron density: 10₉ to 10¹³ cm⁻³, and preferably 10¹⁰ to 10¹² cm⁻³.

Electron temperature: 2 to 9 eV, and preferably 3 to 8 eV.

Wafer temperature: −40 to 100° C., and preferably −30 to 50° C.

Chamber wall temperature: −30 to 300° C., and preferably 20 to 200° C.

Discharge power and bias power vary according to the chamber and electrode sizes. When patterns such as a contact hole and the like are etched on a silicon oxide film and/or a silicon nitride film and/or a silicon-containing, low-dielectric constant film by an inductively coupled plasma (ICP) etching device (chamber volume: 3,500 cm³) designed for small-diameter wafers, the preferable conditions are:

Discharge power: 200 to 1,000 W, and preferably 300 to 600 W; and

Bias power: 50 to 500 W, and preferably 100 to 300 W.

These values increase as the wafer diameter increases.

In the gas plasma of the dry etching gas of the invention, CF₃ ⁺ is selectively generated from CF₃CF fragments, and also radicals derived from the CF₃CF fragments are generated. CF₃ ⁺ improves etching efficiency and is, thereby, capable of etching at a low bias power, resulting in reduced damage to resists and underlying layers such as silicon, etc. The radicals generated from the CF₃CF fragments form an etching reaction layer and a protective layer that are composed of a high density, even fluorocarbon polymer film and increase the etching efficiency of the materials to be etched and protect resists, underlying layers such as silicon and the like, and stopper films such as silicon nitride, silicon carbide and the like. By the irradiation of CF₃ ⁺ that has high etching efficiency onto even, high-density films formed from the radicals derived from CF₃CF, the present invention achieves etching that is well-balanced and free of etch stop, in which the etching rate is only slightly dependent on the size of hole, line or the like.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples and comparative examples are given below to illustrate the invention in more detail.

Example 1 and Comparative Example 1

Using cyclic C₄F₈ (Comparative Example 1) and CF₃CF═CFCF₃ (Example 1) as etching gases, semiconductor substrates with a silicon dioxide (SiO₂) film formed on top of an Si substrate and a resist pattern with a 0.2-μm-diameter hole formed therein were etched to the depth of 1 μm under the conditions of 600 W of IPC (Inductive Coupled Plasma) discharge power, 200 W of bias power, 3 mTorr (0.399 Pa) of pressure, 8×10¹⁰ to 2×10¹¹ cm⁻³ of electron density, and 5 to 7 eV of electron temperature. Table 2 shows the etching rate and the hole diameter (in μm) at the bottom of the 0.2-μm-diameter hole.

TABLE 2 Diameter (μm) at Etching rate the bottom of the of SiO₂ film 0.2-pm-diameter Etching gas (nm/min) hole Comp. c—C₄F₈ 678 0.09 Ex. 1 Ex. 1 CF₃CF = CFCF₃ 643 0.20

While the etching rate of the conventional cyclic C₄F₈ etching gas is higher than that of CF₃CF═CFCF₃, the diameter at the bottom of the hole is 0.10 μm, which is smaller than the diameter at the top of the hole, indicating that the etching is likely to stop. Using CF₃CF═CFCF₃, etching proceeds to the bottom of the hole as is intended for the resist pattern.

Examples 2 and 3, and Comparative Example 1

Using CF₃CF═CF₂ gas alone (when m=0 and Z=F in CF₃CF═CZ_(2−m)(C_(n)F_(2n+1))_(m)), a mixed gas of CF₃CF═CF₂ and CH₂F₂ (flow rate: 45%/55%), and a mixed gas of CF₃CF═CF₂ and CH₂F₂ (flow rate: 20%/80%), contact holes were etched under the conditions of 400 W of ICP (Inductive Coupled Plasma) discharge power, 25 W of bias power and 5 mTorr (0.665 Pa) of pressure. Using a conventional etching gas of a mixed gas of c-C₄F₈, CH₂F₂ and O₂ (flow rate: 17%/76.6%/6.4%), a contact hole was etched under its optimum condition of 400 W of ICP discharge power, 25 W of bias power and 7.5 mTorr (9.975 Pa) of pressure. Table 3 shows the etching rate and the reduction in etching rate by comparing the etching rate with respect to a 0.2-μm-diameter contact hole and a plane surface.

TABLE 3 Etching rate of Reduction Flow rate SiO₂ film in etching Etching gas (%) (nm/min) rate (%) Ex. 2 CF₃CF = CF₂/CH₂F₂ 45/55 375 7 Ex. 3 CF₃CF = CF₂/CH₂F₂ 20/80 317 12 Comp. Ex. 2 c—C₄F₈/CH₂F₂/O₂ 17/76.6/6.4 319 17

Even without adding O₂, the reduction in the etching rate of the CF₃CF═CF₂/CH₂F₂ mixed gas is smaller than that of the c-C₄F₈/CH₂F₂/O₂ mixed gas under its optimum condition. Therefore, the etching gas of the present invention can be suitably used to etch patterns having different sizes at substantially the same etching rate, and minimize the etching time of the underlying layers to produce semiconductor devices with little damage. 

1. A dry etching method comprising etching a silicon material selected from the group consisting of a silicon oxide film, a silicon nitride film by means of a gas plasma of a dry etching gas consisting of (i) CF₃CF═CFCF₃ and (ii) at least one member selected from the group consisting of (CF₃)₂C═O, CF₃CFOCF₂, CF₃CH₂F and CF₂═CFCF═CF₂, wherein CF₃CF═CFCF₃ is used in a flow rate of between 20 and 95%.
 2. A dry etching gas for etching a silicon oxide film and/or a silicon nitride film consisting of (i) CF₃CF═CFCF₃ and (ii) at least one member of gas selected from the group consisting of (CF₃)₂C═O, CF₃CFOCF₂, CF₃CH₂F, and CF₂═CFCF═CF₂, wherein the content of CF₃CF═CFCF₃ in the dry etching gas is between 20 and 95% by volume.
 3. A dry etching method comprising etching a silicon material selected from the group consisting of a silicon oxide film, a silicon nitride film by means of a gas plasma of a dry etching gas consisting of (i) CF₃CF═CFCF₃ and (ii) at least one member selected from the group consisting of (CF₃)₂C═O, CF₃CFOCF₂, CF₃CH₂F and CF₂═CFCF═CF₂, wherein the content of CF₃CF═CFCF₃ in the dry etching gas is between 20 and 95% by volume. 